U.S. patent number 5,626,571 [Application Number 08/565,461] was granted by the patent office on 1997-05-06 for absorbent articles having soft, strong nonwoven component.
This patent grant is currently assigned to The Procter & Gamble Company. Invention is credited to George C. Dobrin, Terrill A. Young.
United States Patent |
5,626,571 |
Young , et al. |
May 6, 1997 |
**Please see images for:
( Certificate of Correction ) ** |
Absorbent articles having soft, strong nonwoven component
Abstract
A nonwoven that is exceptionally soft yet sufficiently strong
for use in absorbent articles is disclosed. The soft, strong
nonwoven includes fibers comprising polyethylene, at least a
portion of which are consolidated. The soft, strong nonwoven has a
cross-machine direction tensile strength of at least about 300 g/in
and a cross-machine direction elongation at break of at least about
40%. The soft, strong nonwoven is preferably formed by permanently
stretching an inelastic base nonwoven in the cross-machine
direction. The preferred base nonwoven has certain properties which
allow it to have sufficient strength after stretching, while being
exceptionally soft, such that the resultant permanently stretched,
soft, strong nonwoven is particularly suitable for use as a
topsheet or a back sheet component in disposable absorbent
articles. More specifically, the preferred base nonwoven has a
cross-machine direction elongation at break of at least about 175%
and a cross-machine direction tensile strength of at least about
400 g/in. A particularly preferred base nonwoven also has a
filament denier of from 1.5 to 10, a basis weight of from 15 to 30
gsy, and, for thermal point bonded nonwovens, a consolidation area
of from 4 to 40%.
Inventors: |
Young; Terrill A. (Cincinnati,
OH), Dobrin; George C. (Cincinnati, OH) |
Assignee: |
The Procter & Gamble
Company (Cincinnati, OH)
|
Family
ID: |
24258709 |
Appl.
No.: |
08/565,461 |
Filed: |
November 30, 1995 |
Current U.S.
Class: |
604/370; 604/358;
442/401; 428/198; 442/394 |
Current CPC
Class: |
B32B
5/26 (20130101); A61F 13/49009 (20130101); Y10T
428/24826 (20150115); Y10T 442/674 (20150401); Y10T
442/681 (20150401) |
Current International
Class: |
A61F
13/15 (20060101); B32B 5/26 (20060101); B32B
5/22 (20060101); D04H 1/54 (20060101); D04H
1/46 (20060101); A61F 013/15 (); A61F 013/20 ();
B32B 027/14 (); D04H 001/04 () |
Field of
Search: |
;604/358,365,366,370,372
;428/198,288,296,365 ;156/167,229,290,296 ;264/288.4,290.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0116845 |
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Aug 1984 |
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EP |
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602613A1 |
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Jun 1994 |
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EP |
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0696654A1 |
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Feb 1996 |
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EP |
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60-181301A |
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Sep 1985 |
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JP |
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62-282003 |
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Dec 1987 |
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JP |
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WO91/18573 |
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Dec 1991 |
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WO |
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WO94/20298 |
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Sep 1994 |
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WO |
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Primary Examiner: Zuttarelli; P.
Attorney, Agent or Firm: Henderson; Loretta J. Miller;
Steven W. Rasser; Jacobus C.
Claims
What is claimed is:
1. A disposable absorbent article comprising a liquid pervious
topsheet, a liquid impervious backsheet, and an absorbent core
disposed between said topsheet and said backsheet, wherein said
topsheet comprises: a apertured nonwoven comprising fibers
comprising polyethylene, at least a portion of said fibers being
consolidated, said nonwoven being permanently mechanically
stretched in the cross-machine direction and having a cross-machine
direction tensile strength of at least about 300 g/in and a
cross-machine direction elongation at break of at least about
40%.
2. The article of claim 1 wherein said nonwoven is formed by
permanently mechanically stretching a base nonwoven comprising
fibers comprising polyethylene, at least a portion of said fibers
being consolidated, said base nonwoven having an elongation at
break of at least about 175% and a cross-machine direction tensile
strength of at least about 400 g/in.
3. The article of claim 2 wherein said base nonwoven has a filament
denier in the range of 1.5 to 10 and a basis weight of from 15
grams/square yard to 30 grams/square yard.
4. The article of claim 3 wherein said base nonwoven has a filament
denier in the range of 2.0 to 3.5 and a basis weight of from 20
grams/square yard to 28 grams/square yard.
5. The article of claim 2 wherein said base nonwoven is permanently
mechanically stretched in the cross-machine direction to at least
about 125% of its unstretched cross-machine direction width.
6. The article of claim 2 wherein said base nonwoven is permanently
mechanically stretched in the cross-machine direction such that the
permanently mechanically stretched nonwoven has effective
apertures.
7. The article of claim 6 wherein said base nonwoven is permanently
mechanically stretched in the cross-machine direction to at least
about 175% of its unstretched cross-machine direction width.
8. The article of claim 1 wherein said fibers of said nonwoven
comprise melt-spunlaid fibers.
9. The article of claim 8 wherein at least a portion of said fibers
are consolidated by thermal spot bonds such that said base nonwoven
has a consolidation area of from about 4% to about 40% of the total
area of said base nonwoven.
10. The article of claim 9 wherein said base nonwoven has a
consolidation area of from about 6% to about 28% of the total area
of said base nonwoven.
11. The article of claim 8 wherein said fibers consist essentially
of polyethylene.
12. A disposable absorbent article comprising:
a liquid impervious backsheet having a garment surface and a body
surface, said backsheet comprising a layer of liquid impervious
polymer material and a nonwoven, said nonwoven comprising fibers
comprising polyethylene, at least a portion of said fibers being
consolidated, said nonwoven being permanently mechanically
stretched in the cross-machine direction and having a cross-machine
direction tensile strength of at least about 300 g/in and a
cross-machine direction elongation at break of at least about 40%,
said nonwoven having a garment surface and a body surface; and
an absorbent core disposed adjacent said body surface of said
backsheet.
13. The article of claim 12 wherein said nonwoven is formed by
permanently mechanically stretching a base nonwoven comprising
fibers comprising polyethylene, at least a portion of said fibers
being consolidated, said base nonwoven having an elongation at
break of at least about 175% and a cross-machine direction tensile
strength of at least about 400 g/in.
14. The article of claim 13 wherein said base nonwoven has a
filament denier in the range of 1.5 to 10 and a basis weight of
from 15 grams/square yard to 30 grams/square yard.
15. The article of claim 14 wherein said base nonwoven has a
filament denier in the range of 2.0 to 3.5 and a basis weight of
from 20 grams/square yard to 28 grams/square yard.
16. The article of claim 13 wherein said base nonwoven is
permanently mechanically stretched in the cross-machine direction
to at least about 125% of its unstretched cross-machine direction
width.
17. The article of claim 12 wherein said fibers of said nonwoven
comprise melt-spunlaid fibers.
18. The article of claim 17 wherein at least a portion of said
fibers are consolidated by thermal spot bonds such that said base
nonwoven has a consolidation area of from about 4% to about 40% of
the total area of said base nonwoven.
19. The article of claim 18 wherein said base nonwoven has a
consolidation area of from about 6% to about 28% of the total area
of said base nonwoven.
20. The article of claim 18 wherein said fibers consist essentially
of polyethylene.
21. The article of claim 12 wherein said backsheet further
comprises a liquid impervious layer of polymeric material disposed
on said garment surface of said nonwoven.
Description
FIELD OF THE INVENTION
The present invention relates to absorbent articles containing a
nonwoven component that has a preferred combination of strength and
softness. In preferred embodiments, the nonwoven is incorporated
into the topsheet or backsheet of the absorbent article.
BACKGROUND OF THE INVENTION
Absorbent articles having nonwoven topsheets and backsheets having
a nonwoven outer layer are known. For example, U.S. Pat. Nos. B1,
3,860,003 (Buell, Apr. 18, 1989) and 5,151,092 (Buell et al., Sep.
29, 1992) disclose disposable absorbent articles having a topsheet
that may be formed from a nonwoven material, and U.S. Pat. No.
4,753,840 (Van Gompel, Jun. 28, 1988) teaches a coated fabric
comprising a base nonwoven ply having a thermoplastic film bonded
thereto.
Nonwovens for topsheet and backsheet applications should have
certain properties suitable for the intended application, for
example, in diapers. First, nonwovens to be used in absorbent
articles should be soft and non-irritating to the wearer. It is
particularly desirable to provide backsheet materials which are
"clothlike," i.e., which are cool to the touch and drapeable.
Second, such nonwovens should have sufficient strength for their
intended application. Thus, the nonwoven should not split or tear
during fabrication or use of the absorbent article. Finally, the
nonwoven should have sufficient coverage or opacity for a given
application. The strength and coverage of a nonwoven depend to a
large extent on the basis weight of the nonwoven. Nonwovens used in
disposable absorbent articles will typically have a basis weight
ranging from about 15 gsy to about 30 gsy in order to provide the
desired strength and coverage. Unfortunately, while strength and
coverage may be increased by an increase in basis weight, the
softness tends to decrease. Thus, it is a particular challenge to
provide nonwovens having each of these properties such that they
are suitable for use in absorbent articles.
One approach to improving the softness of a nonwoven material is
described in U.S. Pat. No. 5,296,289 (Collins, Mar. 22, 1994). It
is an object of U.S. Pat. No. 5,296,289 to provide a spun bonded
nonwoven web which has been stretched to provide a soft "hand" and
greater coverage with minimal sacrifices in strength as a result of
stretching in the machine direction or the cross direction,
although there is a substantial reduction in basis weight of the
web commensurate with the amount of dimensional increases. The
stretchable webs taught by Collins have spot bonds distributed in a
"cornrow" bond pattern. The Collins patent discloses that
stretching of certain prior art nonwoven webs will improve the hand
somewhat, but with unacceptable losses in tensile strength and
elongation characteristics.
While some of the problems of providing functional yet tactilely
acceptable nonwoven materials, topsheets and backsheets have at
least been partially ameliorated by the art, none has solved the
problems in the manner or to the extent of the present
invention.
It is an object of the present invention to provide a nonwoven
which is soft yet which also has sufficient strength and coverage
for use in disposable absorbent articles. It is an additional
object of the present invention to provide disposable absorbent
articles, and particularly backsheets of such articles, having a
clothlike tactile perception.
SUMMARY OF THE INVENTION
The present invention is directed to a nonwoven that is soft yet
sufficiently strong for use in absorbent articles (hereinafter
alternatively referred to as "soft, strong nonwoven"). More
specifically, the present invention relates to nonwovens having
both a cross-machine direction tensile strength of at least about
300 g/in and a cross-machine direction elongation at break of at
least about 40%. Such nonwovens tend to possess a combination of
strength and softness which is preferred for use in disposable
absorbent articles. The soft, strong nonwoven is formed from fibers
of a polymer material, which polymer material includes a
polyethylene polymer segment. At least a portion of the polymeric
fibers are consolidated.
In a preferred embodiment, the soft, strong nonwoven is formed by
permanently mechanically stretching a partially consolidated,
melt-spunlaid base nonwoven formed of fibers of a polymer material
which includes a polyethylene polymer segment and having (1) a
cross-machine direction elongation at break of at least about 175%
and (2) a cross-machine direction tensile strength of at least
about 400 g/in (157 g/cm). Even more preferred base nonwovens have
the additional properties of (3) a filament denier in the range of
1.5 to 10; (4) a basis weight in the range of 15-30 gsy; and, if a
thermal point bonded nonwoven, (5) a consolidation area of from
about 4 to about 40%. It has been found that a base nonwoven having
these properties can be permanently mechanically stretched to
provide relative softness, while retaining sufficient strength such
that it is suitable for use as a topsheet or a backsheet component.
In a particularly preferred embodiment, the base nonwoven has a
cross-machine direction elongation at break of at least about 200%,
more preferably at least about 250%, and a cross-machine direction
tensile strength of at least about 500 g/in, more preferably at
least about 600 g/in.
In preferred embodiments, the soft, strong nonwoven consists
essentially of melt-spun fibers of polyethylene or
polyethylene-polypropylene copolymer. More preferably, the
melt-spun fibers consist essentially of polyethylene. The melt-spun
fibers are preferably consolidated by thermal spot bonds.
The soft, strong nonwoven of the present invention can be
incorporated, for example, into the topsheet or backsheet of an
absorbent article such as diapers, feminine hygiene products,
incontinence products, and the like. The backsheet preferably
comprises the soft, strong nonwoven and a liquid impervious layer,
which layer imparts higher fluid barrier properties to the
nonwoven. The nonwoven is preferably disposed on the garment facing
side of the backsheet to impart a clothlike external surface to the
article.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1-3 are multiple views of a stretching apparatus that may be
used to stretch a base nonwoven as described herein to form the
soft, strong nonwoven of the present invention.
FIG. 4 is a plan view of a diaper according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The soft, strong nonwoven is formed from fibers of a polymer
material, which polymer material includes ethylene repeating units
(--CH.sub.2 --CH.sub.2 --) to form a polyethylene segment. The
polymer material can be polyethylene, a copolymer of polyethylene,
or a mixture of these polymeric materials. By "copolymer," it is
intended to encompass polymers formed by the copolymerization of
ethylene or polyethylene with one or more other suitable monomers
or polymers such that the resultant copolymer contains repeating
ethylene units. Suitable other monomers and polymers include
C.sub.3 -C.sub.6 polyolefins, such as propylene, butylene, and the
like, and polymers thereof, for example, polypropylene. In a
preferred embodiment, the fibers are formed of polyethylene. Such
polyethylene fibers may be, for example, linear low density
polyethylene fibers or high density polyethylene fibers. Thus, the
polymeric fibers can have a density ranging from 0.91 g/cc to 0.97
g/cc. The polymeric fibers can be prepared by several methods such
as are known in the art, including melt-spinning processes and
solution-spinning processes.
The polymeric fibers can be formed into a nonwoven web by methods
such as are now known or become known in the art of forming fibrous
nonwoven webs in which the fibers are at least partially
consolidated. For example, the fibers can be spun and deposited on
a suitable web-forming substrate in a continuous process to form a
fibrous web (i.e., spun laid), followed by consolidation.
Alternatively, polymeric fibers can be spun into tow and cut apart
to form staple fibers, which are then formed into a fibrous web by
a suitable technique, followed by consolidation. The fibers can be
spunlaid or spun into tow by melt-spinning or solution spinning
processes. In a preferred embodiment, the fibers are spunlaid or
spun into tow by a melt-spinning process.
A melt-spun laid nonwoven can be formed by extruding a line of
spaced molten synthetic filaments of the polymer through a
spinnerette having a plurality of juxtaposed openings to provide a
plurality of spaced non-solidified filaments, as is taught in U.S.
Pat. No. 3,509,009 issued to Hartmann on Apr. 28, 1970 and
incorporated herein by reference. The filaments are immediately
seized on both sides by heated gas currents and carried away
without breaking off, so that the filament diameters decrease
within a distance of about 1 cm from the spinnerette, and so that
the filaments are not fully drawn. The filaments are subsequently
deposited on a foraminous moving wire in random orientation or
winding entanglement, but substantially in the machine
direction.
Staple fibers can be formed by extruding a plurality of spaced
molten synthetic filaments of the polymer through a spinnerette
having a plurality of juxtaposed openings to provide a plurality of
spaced non-solidified filaments (tow), followed by chopping or
cutting the tow to form discontinuous fibers (staple fibers). A web
is formed by laying the staple fibers onto a suitable substrate.
The web can be formed by any suitable method such as are known in
the art, for example, carding, air-laying, wet-laying and the like.
In a preferred embodiment, the staple fibers are carded and
air-laid onto a suitable substrate. As prepared on conventional
carding equipment, the fibers in the resultant fibrous web are
substantially oriented in the machine direction.
The fibers of the melt-spunlaid, carded, or otherwise formed web
are then at least partially consolidated to form a nonwoven useful
in the present invention. As used herein "consolidation,"
consolidated and the like refers to the bringing together of at
least a portion of the fibers into closer proximity to form sites
which function to increase the resistance of the nonwoven to
external forces, e.g., tensile forces, as compared to the
unconsolidated web. "Partially consolidated" refers to the presence
of numerous spaced apart sites (i.e., intermittent sites), in
contrast to a nonwoven which is consolidated such that individual
sites are not perceived by simple magnification.
Consolidation can be caused by any suitable method that applies
heat and/or pressure to the fibrous web. Consolidation methods
include thermal spot (i.e., point) bonding and hydroentanglement.
Thermal point bending can be accomplished by passing the fibrous
web through a pressure nip formed by two rolls, one of which is
heated and contains a plurality of raised points on its surface, as
is described in U.S. Pat. No. 3,855,046 issued to Hansen et al. on
Dec. 17, 1974, incorporated herein by reference. The heated roll is
heated to a temperature sufficient to cause thermoplastic flow or
melting of the polymer in the regions of the web corresponding to
the raised points as the web passes through the nip, with the sites
being formed where thermoplastic flow occurs. Hydroentanglement
typically involves treatment of the fibrous web with high pressure
water jets to consolidate the web via mechanical fiber entanglement
(friction) in the region desired to be consolidated, with the sites
being formed in the area of fiber entanglement. The fibers can be
hydroentangled as taught in U.S. Pat. Nos. 4,021,284 issued to
Kalwaites on May 3, 1977 and 4,024,612 issued to Contractor et al.
on May 24, 1977, both incorporated herein by reference. In the
presently preferred embodiment, the polymeric fibers of the
nonwoven are consolidated by thermal point bonds.
Nonwovens that are consolidated by thermal point bonds can be
characterized by a consolidation area. As used herein, the
"consolidation area" refers to the area occupied by the sites
formed by bringing the fibers into relatively close proximity
(hereinafter alternatively referred to as "bond sites"), based on
the total area of the nonwoven. The thermal point bonded nonwovens
useful in the present invention may have a consolidation area of
less than 40%. The consolidation area is determined with a simple
microscope (e.g., 10-30.times.) having a measuring scale that
enables measurement of the bond sites when viewed through the
microscope (e.g., ruled at about 0.002"). A sample of the nonwoven
is viewed through the microscope and the number and size of bond
sites is measured for four different 0.5".times.0.5" areas in view.
The area occupied by the sites in each (0.5") square area is
determined mathematically, with the consolidation area being the
average of the four calculations.
Consolidation by hydroentanglement is influenced by the number and
placement of water jets relative to the nonwoven web being
consolidated, and the force being exerted on the nonwoven by the
individual jets. The consolidation of a hydroentangled nonwoven
tends to increase with an increase in the number of water jets,
with nearer placement of the jets relative to the nonwoven web, or
with an increase in the pressure exerted by the water jets.
The nonwovens have a tensile strength of at least 300 g/in and an
elongation at break of at least about 40%, each being in the
cross-machine direction. It has been found that a nonwoven having
these properties tends to have a combination of strength and
softness that is preferred for use in absorbent articles. The soft,
strong nonwoven preferably also has a filament denier in the range
of 1.5 to 10; a basis weight in the range of 10-20 gsy; and, for
thermal point bonded nonwovens, a consolidation area of less than
about 40%. The soft, strong nonwoven having these properties can be
directly formed from the polymeric material by the above-described
processes, with the process variables being controlled in
conventional manner to provide the desired denier, basis weight and
consolidation area.
As understood by the skilled artisan, the filament denier refers to
the number of grams of a given fiber material in 9000 meters of
length of the material, which is determined primarily by the
polymer extrusion rate and degree of attenuation of the spun fibers
making up the nonwoven. In general, the fiber denier increases with
an increase in the extrusion rate or with a decrease in degree of
attenuation decreases. Fiber denier can be measured according to
ASTM D 1907/D3218, incorporated herein by reference.
Basis weight is a well known term in the art used to designate the
weight of a nonwoven web per unit area of the web. As used herein,
a "web" of fibrous material such as the nonwovens herein described
is a sheet of thin, substantially contiguous fibrous material
having two substantially parallel surfaces. Although a web of
fibrous material need not be flat or smooth, theoretically, it is
or can be laid out in a substantially planar, two-dimensional
arrangement of indefinite length and indefinite width projecting in
the two dimensions. The basis weight is determined based on a
selected area defined by these two dimensions. The basis weight is
determined by the weight of fibers laid down on a forming substrate
per unit area, and is primarily a function of the fiber density,
fiber denier and substrate speed relative to the apparatus used to
lay down the fibers onto the substrate. In general, the basis
weight increases with an increase in fiber density or fiber denier,
or with a decrease in the substrate speed. The basis weight can be
measured by ASTM D3776-85 Option B, incorporated herein by
reference.
The consolidation area for thermally point bonded nonwovens is
influenced by the number and placement of raised points on the roll
used to form the thermal point bonds. In general, as the number of
raised points per unit area increases, the consolidation area of
the nonwoven increases.
Tensile strength and elongation at break as used herein refer to
the respective properties as measured according to ASTM D1682-64
and 7.1.2.2, incorporated herein by reference. For webs formed of
the preferred polymeric fibers described herein, these tensile
properties are primarily influenced by the basis weight and the
consolidation of the nonwoven. In general, tensile strength tends
to increase with an increase in basis weight and/or consolidation.
On the other hand, elongation at break tends to decrease with an
increase in basis weight and/or consolidation.
In a preferred embodiment, the soft, strong nonwoven is formed by
permanently mechanically stretching, in the cross-machine direction
and optionally the machine direction, a base nonwoven having (1) a
cross-machine direction tensile strength of at least about 400 g/in
(157 g/cm); and (2) a cross-machine direction elongation at break
of at least about 175%.
"Machine direction" (alternatively referred to herein as "MD") is a
well known term of art that is generally understood to refer to the
direction corresponding to the length of the nowoven as it is
formed in conventional nonwovens forming apparatii. The machine
direction typically corresponds to the direction of fiber
orientation as they are laid down to form the nonwoven.
"Cross-machine direction" (alternatively referred to herein as
"CD") refers to the direction which is 90.degree. to the machine
direction. The nonwoven is substantially formed in a plane defined
by the machine and cross-machine directions.
Preferred base nonwovens also have a filament denier in the range
of 1.5 to 10; a basis weight in the range of 15 gsy to 30 gsy; and,
for thermal point bonded nonwovens, a consolidated bond area of
from about 4 to about 40%. It has been found that a base nonwoven
having these properties can be permanently mechanically stretched
to provide a nonwoven that is soft yet sufficiently strong such
that it is suitable for use as a topsheet or a backsheet component.
In a particularly preferred embodiment, the base nonwoven has a
cross-machine direction tensile strength of at least about 500
g/in, more preferably at least about 600 g/in, and a cross-machine
direction elongation at break of at least about 200%, more
preferably at least about 250%.
The base nonwoven that is to be permanently mechanically stretched
is inelastic. As used herein, "inelasticity" refers to the failure
of a material, upon being subjected to a tensile force, to
substantially recover to its original state of zero elongation
after the tensile force is removed. The base nonwoven of the
present invention, upon being subjected to a tensile force to cause
50% elongation, will typically fail to recover to an elongation of
less than 20%. The inelasticity of the nonwoven is primarily
influenced by the polymeric material making up the fibers of the
nonwoven.
The base nonwoven that is to be permanently mechanically stretched
and having the aforementioned properties can be directly formed
from the polymeric material by the processes described herein, with
the process variables being controlled in conventional manner to
provide the desired denier, basis weight and consolidation area.
These variables are influenced in the manner previously described
and can be controlled by the skilled artisan in light thereof.
Melt-spunlaid nonwovens formed from polyethylene fibers and having
the aforementioned, base nonwoven properties of tensile strength,
elongation at break, denier, basis weight, consolidation area and
inelasticity and which can be permanently mechanically stretched in
accordance with the present invention are commercially available
from Polybond Co. of Waynesboro, Va., as #86964-S, and from Corovin
of Peine, Germany, as Corolind 16714.
When a carded and hydroentangled nonwoven is employed as a base
nonwoven which is to be permanently mechanically stretched, higher
basis weights tend to be necessary in order for the stretched
nonwoven to have the desired cross-machine direction tensile
strength of at least about 300 g/in, as compared to a base nonwoven
which is melt-spunlaid and thermally spot-bonded. For example, the
basis weight of a carded and hydroentangled base nonwoven which
provides this tensile strength after stretching is typically in the
range of from about 30 gsy to about 50 gsy. Due to the higher cost
of higher basis weight materials, a soft, strong nonwoven of the
present invention formed from such a carded and hydroentangled base
nonwoven is not preferred.
The soft, strong nonwoven formed by permanently mechanically
stretching the above-described base nonwoven unexpectedly exhibits
certain properties relative to the soft, strong nonwoven which is
directly formed by conventional nonwoven processes. More
specifically, the permanently mechanically stretched, soft, strong
nonwoven exhibits higher toughness and elasticity. Thus, the
permanently mechanically stretched nonwoven tends to withstand
sudden tensile forces, such as may be experienced in the wearing of
disposable articles. The permanently mechanically stretched, soft,
strong nonwoven may also be economically preferred over the
nonwoven which is directly formed.
Permanent mechanical stretching in the cross-machine direction may
involve a number of mechanisms. Typically, a substantial portion of
the fibers of the nonwoven are reoriented toward the cross-machine
direction. The fibers in the consolidated fiber sites may slip from
the site, be stretched relative to the site, or break away from the
site. The resultant soft, strong nonwoven has a basis weight that
is from about 50% to about 90% of the basis weight of the base
nonwoven. Thus, the resultant nonwoven typically has a basis weight
of from about 7.5 gsy to about 27 gsy, preferably about 10 gsy to
about 20 gsy.
Cross-machine direction stretching can be caused to varying degrees
depending on the required end use strength and coverage, provided
that the nonwoven has, after stretching, a cross-machine direction
tensile strength of at least about 300 g/in and an elongation at
break of at least about 40%. In general, the softness of the
nonwoven tends to increase with increasing levels of permanent
stretching. The base nonwoven is typically permanently stretched in
the CD to at least about 125%, preferably 175%, of its original,
unstretched CD width. Very soft yet sufficiently strong nonwovens
have been obtained by permanently stretching the base nonwoven to
at least about 200% of its original, unstretched CD width.
In one embodiment of the present invention, stretching is
relatively aggressive to thereby form effective apertures in at
least a portion of the nonwoven. When the resultant nonwoven is
employed as a topsheet in disposable absorbent articles, the
apertures tend to improve the rate of acquisition of relatively
viscous body fluids such as menses or runny feces. As used herein,
"effective apertures," refers to apertures which provide a
significant increase in the rate of acquisition of one or more of
such relatively viscous body fluids. The apertures may be areas of
decreased web basis weight (relative to other areas of the
stretched web, excluding the bond sites), including areas which are
substantially fiber free. In general, as the aperture size
increases, the apertures tend to be more effective in increasing
the rate of acquisition of relatively viscous body fluids. The size
of the apertures tends to increase with increasing levels of
permanent stretching. The size of the apertures is also influenced
by the pattern of the consolidated areas in the nonwoven, including
the frequency and size of the consolidated fiber sites. In general,
the fewer or the smaller the consolidated fiber sites, the smaller
the possible size of the apertures.
Nonwovens having apertures useful for topsheet applications are
typically obtained by permanently stretching the base nonwoven in
the CD to at least about 175% of its original, unstretched CD
width, leaving the relaxed, permanently stretched nonwoven to have
at least about 140% of its original CD width. More preferably, the
apertured nonwovens are formed by stretching the base nonwoven to
from about 200% to about 300% of its original, unstretched CD
width. For example, permanently stretching a base nonwoven as
described above from about 175% to about 300% of its original CD
width has provided aperture areas of about 0.0008 in.sup.2 to about
0.003 in.sup.2 at a density of about 5 to about 30 per in.sup.2 of
nonwoven, which is effective in increasing the rate of acquiring
runny feces.
The cross-machine direction stretching can be substantially uniform
throughout the nonwoven. Alternatively, only a portion or
discontinuous portions of the base nonwoven may be stretched in the
cross-machine direction. For example, the base nonwoven can be CD
stretched along only a central, CD portion of the base nonwoven
along the MD of the nonwoven. The resultant permanently stretched
base nonwoven has a central, CD, relatively soft portion having
longitudinal edges running in the MD, and substantially unstretched
portions bordering the longitudinal edges. The resultant
permanently stretched nonwoven can be used as a topsheet in
disposable absorbent articles, where the relatively soft portion is
positioned to include the acquisition region of the topsheet when
in use, and the substantially unstretched portions are positioned
in the regions of the absorbent article where higher strength
materials may be desired, e.g., in the ears and along the side
edges of the absorbent article. In an economically preferred
embodiment, the relatively soft portion comprises a continuous
strip running between the end edges of the topsheet of the
disposable absorbent article. Alternatively, the relatively soft
portion may substantially correspond to the acquisition region of
the article when in use.
The base nonwoven is permanently stretched by the stretching
operation. By "permanently stretched," it is meant that the
nonwoven evidences permanent deformation in the direction of
stretch when elongated to at least 50% of its original dimension in
the direction of stretch. Thus, upon being subjected to a tensile
force to cause at least 50% elongation in the direction of stretch,
the base nonwoven fails to recover to an elongation of less than
20% in the direction of stretch after the force is removed.
Typically, the base nonwoven retains at least about 90% of the
maximum elongation after removal of the force.
The base nonwoven can be stretched in the cross-machine direction
by any method that is now known or becomes known in the art,
provided that the method does not result in damage to the nonwoven
such that the nonwoven is unsuitable for its intended application.
Exemplary methods include stretching with Mt. Hope rolls, bowed
rolls, meshing platens, or intermeshing grooved or corrugated
combining rolls. The base nonwoven can be stretched to the desired
maximum elongation in a single step, or sequentially by several
steps of incrementally increasing elongation force. In a preferred
embodiment, the base nonwoven is incrementally stretched, for
example, as described in U.S. Pat. No. 5,143,679, issued to Weber,
et al. on Sep. 1, 1992.
Suitable methods and apparatus for mechanically stretching
nonwovens, or for mechanically stretching portions of a diaper,
which methods and apparatus are suitable for used herein for
mechanically stretching the base nonwoven, are contained in the
U.S. Pat. Nos. 2,075,189, issued to Galligan, et al. on Mar. 30,
1937; 3,025,199, issued to Harwood on Mar. 13, 1962; 3,624,874,
issued to Lauchenauer, et al. on Dec. 7, 1971; 4,107,364, issued to
Sisson on Aug. 15, 1978; 4,209,563, issued to Sisson on Jun. 24,
1980; 4,517,714, issued to Sneed et al. on May 21, 1985; 4,834,741,
issued to Sabee on May 30, 1989; the above referenced 5,143,679;
5,156,793, issued to Buell, et al. on Oct. 20, 1992; and 5,167,897,
issued to Weber, et al. on Dec. 1, 1992. The disclosures of each of
these patents are hereby incorporated herein by reference in their
entirety.
Particularly preferred apparatus and methods which can be used to
mechanically stretch the nonwoven are disclosed in the
above-referenced U.S. Pat. Nos. 4,834,741; 5,143,679; 5,156,793;
and 5,167,897.
For example, the nonwoven can be stretched using an apparatus as
described in U.S. Pat. No. 4,834,741. As described in this patent
and shown in FIGS. 1-3, a suitable apparatus 100 has a pair of
cooperating corrugating (or pleating) rolls 10, through which the
nonwoven 20 is passed in the machine direction in order to
permanently stretch the nonwoven 20 in the CD. The nonwoven is
suitably supplied to the apparatus 100 from a supply (unwind) roll
(not shown). Each of the corrugating rolls 10 has a transverse
raised portion 12 that extends partially around the roll
circumference. The raised portions 12 define corrugated surfaces 14
that mesh with each other with only a small radial clearance
therebetween. The rolls 10 rotate together in the direction of
arrows 16 and in timed relation to the movement of the nonwoven 20
such that only the portions of the nonwoven 20 desired to be CD
stretched passes between the corrugated surfaces 14. The developed
transverse length of the corrugated surfaces 14 is substantially
greater than the width of the nonwoven 20. Consequently, the
nonwoven 20 is stretched or expanded transversely across the
nonwoven as it passes between the corrugated surfaces 14.
The degree of stretch can be controlled by controlling the radial
clearance between the intermeshing corrugated surfaces, with the
degree of stretch increasing with a decreasing clearance.
Alternatively, the nonwoven can be directed through an incremental
web stretching system employing opposed pressure applicators having
three dimensional surfaces which at least to a degree are
complementary to one another, such as described in the above
referenced and incorporated U.S. Pat. Nos. 5,143,679; 5,156,793;
and 5,167,897.
Thus, the untensioned, base nonwoven web may be passed between
corrugated or grooved uppermost corrugated rolls and corrugated or
grooved lowermost corrugated rolls. While the exact configuration,
spacing and depth of the complementary grooves on the uppermost and
lowermost corrugated rolls will vary, depending upon such factors
as the amount of permanent stretch desired in the final nonwoven
web, two pairs of sequenced corrugated rolls, each having a
peak-to-peak groove pitch of approximately 0.150 inches, an
included angle of approximately 12 degrees as measured at the peak,
and a peak-to-valley groove depth of approximately 0.300 inches
have been employed in a particularly preferred embodiment of the
present invention. The exterior peak of each corrugation on the
aforementioned corrugated roll pairs exhibits a radius of
approximately 0.010 inches, while the internal groove formed
between adjacent corrugations typically exhibits a radius of
approximately 0.040 inches. The sequenced corrugated roll pairs are
typically adjusted so that the opposing peaks on each succeeding
pair of meshing corrugated rolls increase their degree of overlap
with one another approximately 0.035-0.050 inches from the first
pair of meshing corrugated rolls to the second pair, the second set
of meshing corrugated rolls typically overlapping one another to a
total depth between about 0.150 inches and about 0.175 inches. Two
pairs of meshing corrugated rolls of the aforementioned type
mounted in sequence with one another have produced a permanently
stretched, soft, strong nonwoven having good integrity.
The degree of overlap of the opposing peaks on the successive pairs
of meshing corrugated rolls may of course be adjusted, as desired,
to produce more or less permanent stretch or apertures in the
nonwoven web. For the aforementioned roll geometry and laminate web
construction, peak-to-peak overlap depths ranging from as little as
about 0.050 inches to as much as about 0.225 inches are feasible.
In general, as the number of sequenced meshing corrugated roll
pairs increases for any given total mount of incremental
stretching, the potential for web damage decreases. This is
believed due to the fact that the incremental stretching operation
is carried out more gradually in a series of relatively small steps
when a series of sequenced meshing corrugated roll pairs is
employed. More gradual stretching of the nonwoven web is believed
to minimize damage to the web, especially in the case of webs with
a CD elongation at the lower end of the acceptable range defined
herein.
The incremental web stretching system is preferably equipped with
active vacuum ports and vacuum manifolds such as described in U.S.
Pat. No. 5,143,679 to exert suction against the nonwoven web it is
acted upon by the uppermost grooved/corrugated rolls. As further
described therein, the vacuum ports on the lowermost rolls are
preferably covered by a porous material, such as 0.090" mesh
honeycomb, to provide support to the portions of the nonwoven web
acted upon by the vacuum and to provide a good gripping surface
against the web so as to substantially prevent lateral slippage or
movement of the web across the honeycomb surface whenever the web
is acted upon by vacuum.
Under optimum circumstances, the maximum degree of permanent
stretch which can be imparted to the nonwoven web is determined by
the depth of engagement between the grooves on the uppermost
corrugated rolls and the grooves on the lowermost corrugated rolls.
However, unless the nonwoven web is substantially prevented from
slipping or contracting in a direction substantially parallel to
the direction of web stretching as it passes between the meshing
corrugated rolls, the optimum degree of incremental, permanent
stretching is not realized. Therefore, in its most preferred form,
the incremental web stretching operation is carried out while the
outermost portions of the nonwoven web are subjected to restraint,
to substantially prevent the nonwoven web from slipping or
contracting in a direction parallel to the desired direction of
stretching as it passes between the sets of sequentially positioned
meshing corrugated rolls. In addition, vacuum ports may be used to
hold the nonwoven e.g., as described in U.S. Pat. No.
5,143,679.
Sequentially stretching the nonwoven web using multiple pairs of
meshing corrugated rolls, each subsequent pair of corrugated rolls
exhibiting an increased degree of meshing, reduces the rate at
which the elongation process is carried out and hence the rate at
which strain is experienced by the nonwoven web as it passes
therebetween. In addition, the temporary release of tension from
the web as it passes between the successive roll pairs allows some
degree of stress redistribution to occur in the web prior to the
web's being incrementally stretched to a greater degree by each
succeeding roll pair.
Therefore, the more meshing roll pairs which are used to achieve
the desired degree of incremental stretching, the more gradual will
be the stretching of the web as it passes between any given roll
pair and the more opportunities there will be provided for stress
redistribution to occur within the web. This not only minimizes the
rate at which strain is experienced by the nonwoven web, but
maximizes the opportunities for stress redistribution between each
incremental stretching operation. Consequently such a sequential
roll system is less prone to cause damage to the webs being
processed than if the entire stretching operation is carried out on
a single roll pair exhibiting an equivalent degree of meshing.
For CD stretching, the sequentially positioned pairs of meshing
corrugated rolls have their corrugations aligned substantially
parallel to one another and to the direction of nonwoven supply
feed (MD). Stretching of the nonwoven web in other directions may
be accomplished by employing sequentially positioned pairs of
corrugated rolls wherein the corrugations are not all oriented
parallel to one another. Furthermore, the corrugations on such
sequentially positioned pairs of corrugated rolls need not
necessarily be aligned parallel to either the machine or the
cross-machine direction. For example, the meshing teeth on the
sequentially posilioned pairs of corrugated rolls employed to
sequentially stretch the nonwoven web may be arrayed in a
curvilinear configuration to produce permanent stretch along the
curvilinear contour rather than in a straight line.
In one embodiment of this invention, the cross-machine direction
stretched nonwoven is subsequently stretched in the machine
direction or in one or more directions oblique to the machine
direction. It has been found that stretching of the base nonwoven
solely in the machine direction tends to destroy the nonwoven.
Machine direction stretching can be accomplished using any of the
methods such as are known in the art. For example, meshed platens
or intermeshing grooved or corrugated rolls such as previously
described herein may be used.
After stretching, the nonwoven has diminished yet sufficient
coverage and strength for use in disposable absorbent articles. The
cross-machine direction tensile strength of the stretched nonwoven
is at least about 300 g/in, preferably at least about 500 g/in. The
cross-machine direction % elongation at break tends to be higher
than the unstretched, base nonwoven and is typically at least about
225%. The preferred nonwoven is softer and less strong in the
central region than along the edges. Such nonwovens can be obtained
by permanently mechanically stretching only an interior portion of
the width of the nonwoven.
Nonwovens as formed from the polymeric material having a
polyethylene segment tend to be hydrophobic. In certain
applications it may be desired to treat the nonwoven to render at
least a portion of the nonwoven hydrophilic. For example, for
topsheet applications in disposable absorbent articles such as
described herein, it is preferred that at least the upper surface
of the topsheet be hydrophilic so that liquids will transfer
through the topsheet more rapidly. This diminishes the likelihood
that body exudates will flow off the topsheet rather than being
drawn through the topsheet and being absorbed by the absorbent
core. The nonwoven can be rendered hydrophilic by treating it with
a surfactant. Suitable methods for treating the nonwoven with a
surfactant include spraying the nonwoven material with the
surfactant and immersing the nonwoven into the surfactant. A more
detailed discussion of such a treatment and hydrophilicity is
contained in U.S. Pat. No. 4,988,344 entitled "Absorbent Articles
with Multiple Layer Absorbent Layers" issued to Reising, et al. on
Jan. 29, 1991; U.S. Pat. No. 4,988,345 entitled "Absorbent Articles
with Rapid Acquiring Absorbent Cores" issued to Reising on Jan. 29,
1991; U.S. Pat. No. 4,950,264 entitled "Thin, Flexible Sanitary
Napkin" issued Osborn on Aug. 21, 1990; and in U.S. Pat. No.
5,009,653 entitled "Thin, Flexible Sanitary Napkin" issued to
Osborn on Apr. 23, 1991; each of which is incorporated by reference
herein. The nonwoven can be treated either before or after any
mechanical stretching operations described herein. In a preferred
embodiment, the nonwoven is treated before any mechanical
stretching operations.
The soft, strong nonwoven of the present invention can be combined
with a liquid impervious layer of polymeric material to improve the
fluid barrier properties of the nonwoven. By "liquid impervious,"
it is meant that the layer of polymeric material resists the
transport of liquids through the layer under the conditions of
normal use of the application for which the product incorporating
the nonwoven is intended. For example, for disposable absorbent
articles such as those described herein, the layer of polymeric
material resists the transport of body fluids through the layer,
under normal wearing conditions of the absorbent article.
Suitable polymeric materials for forming the liquid impervious
layer include relatively non-elastic materials, for example,
conventional polyolefins such as polyethylene, polypropylene, and
the like, and copolymers and blends thereof. Conventional
polyolefins are commercially available, for example, from the Dow
Chemical Company and Exxon under the trade names Insight and Exact,
respectively. Alternatively, the polymeric material can be
elastomeric. Suitable elastomeric polymers include those
commercially available from the Shell Chemical Companyunder the
trade name of KRATON.RTM. (synthetic rubber triblock polymers,
e.g., styrene-polyisoprenestyrene triblock polymers, polyurethanes,
polyolefins such as those commercially available from Himontunder
the trade name CATALLOY.RTM. and blends of such polyolefins with
conventional polyolefins. The polymeric material can be degradable,
for example, a photodegradable, hydrodegradable or biodegradable
material.
The nonwoven can be combined with the polymeric material by any
suitable method to form a liquid impervious layer of the polymeric
material on the nonwoven. Suitable techniques include coating or
lamination techniques such as are known in the art. Preferred
laminates are adhesively bonded together, e.g., with hot melt
adhesives. Adhesive bonding can be achieved through a variety of
techniques such as are known in the art, e.g., slot extruder
coating, or printed, sprayed or spiraled adhesive coating. Sonic
lamination and extrusion coating of the polymeric material and the
nonwoven are also applicable but are less preferred.
The nonwoven that is combined with the polymeric material can be
mechanically stretched. Mechanical stretching may be perfondled to
improve softness, drapeability, toughness, or to improve the bulk
of the resultant product. Stretching may be accomplished, for
example, by any of the methods and apparatus previously described
in relation to stretching of the base nonwoven.
The soft, strong nonwoven of the present invention is particularly
suitable for use as a component in disposable absorbent articles.
However, it is to be understood that the soft, strong nonwoven,
including such a nonwoven combined with a polymerie material, may
have utility in other applications, for example, disposable table
cloths, napkins, surgical drapes, bibs and the like.
As used herein, the term "absorbent article" refers to devices
which absorb and contain body exudates, and more specifically,
refers to devices which are placed against the skin of a wearer to
absorb and contain the various exudates discharged from the body.
The term "disposable" is used herein to describe absorbent articles
which are not intended to be laundered or otherwise restored or
reused as an absorbent article after a single use. Examples of
disposable absorbent articles include feminine hygiene garments
such as sanitary napkins and panti-liners, diapers, incontinence
briefs, diaper holders, training pants, and the like.
Disposable absorbent articles typically comprise a liquid pervious
topsheet, a liquid impervious backsheet joined to the topsheet and
an absorbent core positioned between the topsheet and the
backsheet. Disposable absorbent articles and components thereof,
including the topsheet, backsheet, absorbent core, and any
individual layers of these components, have a body surface and a
garment surface. As used herein, "body surface" means that surface
of the article or component which is intended to be worn toward or
adjacent to the body of the wearer, while the "garment surface" is
on the opposite side and is intended to be worn away from the
wearer's body or placed adjacent to the wearer's undergarments when
the disposable absorbent article is worn. The soft, strong nonwoven
of the present invention is particularly useful for use in the
topsheet or the backsheet of disposable absorbent articles.
The following description generally discusses the absorbent core,
topsheet, and backsheet materials that are useful in disposable
absorbent articles. It is to be understood that this general
description applies to these components of the specific absorbent
article shown in FIG. 4 and further described below, in addition to
those of other disposable absorbent articles which are generally
described herein.
The absorbent core is capable of absorbing or retaining liquids
(e.g., menses, urine, and/or other body exudates). The absorbent
core is preferably compressible, conformable, and non-irritating to
the wearer's skin. The absorbent core may be manufactured in a wide
variety of sizes and shapes (e.g., rectangular, oval, hourglass,
"T" shaped, dog bone, asymmetric, etc.). The absorbent core may
include any of a wide variety of liquid-absorbent materials
commonly used in absorbent articles, such as comminuted wood pulp,
which is generally referred to as airfelt. Examples of other
suitable absorbent materials for use in the absorbent core include
creped cellulose wadding; meltblown polymers; coform; chemically
stiffened, modified or cross-linked cellulosic fibers; synthetic
fibers such as crimped polyester fibers; peat moss; tissue
including tissue wraps and tissue laminates; absorbent foams;
absorbent sponges; superabsorbent polymers; absorbent gelling
materials; or any equivalent material or combinations of materials,
or mixtures of these. The configuration and construction of the
absorbent core may also be varied (e.g., the absorbent core may
have varying caliper zones and/or have a profile so as to be
thicker in the center; hydrophilic gradients; superabsorbent
gradients; or lower average density and lower average basis weight
zones, e.g., acquisition zones; or may comprise one or more layers
or structures). The total absorbent capacity of the absorbent core
should, however, be compatible with the design loading and the
intended use of the absorbent article. Further, the size and
absorbent capacity of the absorbent core may be varied to
accommodate different uses such as diapers, incontinence pads,
pantiliners, regular sanitary napkins, and overnight sanitary
napkins, and to accommodate wearers ranging from infants to
adults.
The topsheet is preferably compliant, soft feeling, and
non-irritating to the wearer's skin. Further, the topsheet is
liquid pervious, permitting liquids (e.g., menses and/or urine) to
readily penetrate through its thickness.
The backsheet is impervious to liquids (e.g., menses and/or urine)
and preferably comprises a thin plastic film, although other
flexible liquid impervious materials may also be used. As used
herein, the term "flexible" refers to materials which are compliant
and will readily conform to the general shape and contours of the
human body. The backsheet prevents the exudates absorbed and
contained in the absorbent core from wetting articles which contact
the absorbent article such as bedsheets, pants, pajamas and
undergarments. Further, the backsheet may permit vapors to escape
from the absorbent core (i.e., the backsheet is breathable) while
still preventing exudates from passing through the backsheet. The
size of the backsheet is dictated by the size of the absorbent core
and the exact absorbent article design selected. Various topsheet
and backsheet materials are well known in the art. In the
disposable absorbent articles of the present invention, either the
topsheet, backsheet or both include the soft, strong nonwoven of
the present invention.
The soft, strong nonwoven of the present invention provides a
topsheet that is especially soft and non-irritating to the wearer,
thereby increasing wearer comfort. In addition, where the topsheet
comprises a permanently stretched, soft, strong nonwoven having
apertures as described herein, the topsheet is particularly
effective for acquiring large insults of bodily fluids or highly
viscous bodily excretions such as runny feces or menses. The
permanently stretched, soft, strong nonwoven of the present
invention also tends to have a greater thickness than the
unstretched base nonwoven, thereby providing a pleasing esthetic
appearance.
Even more preferred backsheels include the soft, strong nonwoven in
combination with a polymeric film as previously described. In a
particularly preferred embodiment, the backsheet comprises the
nonwoven disposed on the garment facing side of the polymeric film.
Alternatively, the nonwoven can be disposed on the body facing side
of the polymeric film, or the nonwoven can be disposed on both the
body facing side and the garment facing side of the polymeric film.
The backsheet comprising the soft, strong nonwoven of the present
invention is particularly soft as compared to previously known
clothlike backsheets. In addition, such a backsheet tends to have a
higher energy to break, which provides resistance to splitting such
as may otherwise occur when the wearer exerts a high speed force on
the component, as when rapidly sitting down. Polymeric films that
can be used as a component of the backsheet include thermoplastic
films of polyethylene or polypropylene. For example, a suitable
polyethylene films may havea thickness of from about 0.012 mm (0.5
mil) to about 0.051 mm (2.0 mils). Exemplary polyethylene films are
manufactured by Clopay Corporation of Cincinnati, Ohio, under the
designation P18-1401 and by Tredegar Film Products of Terre Haute,
Ind., under the designation XP-9703. A backsheet comprising a
polymeric film may be embossed and/or matte finished to provide a
more clothlike appearance to the polymeric film.
The backsheet and the topsheet are positioned adjacent the garment
surface and the body surface, respectively, of the absorbent core.
The absorbent core is preferably joined with the topsheet, the
backsheet, or both in any manner as is known by attachment means
(not shown in FIG. 4) such as those well known in the art. However,
embodiments of the present invention are envisioned wherein
portions of the entire absorbent core is unattached to either the
topsheet, the backsheet, or both.
For example, the backsheet and/or the topsheet may be secured to
the absorbent core or to each other by a uniform continuous layer
of adhesive, a patterned layer of adhesive, or an array of separate
lines, spirals, or spots of adhesive. Adhesives which have been
found to be satisfactory are manufactured by H. B. Fuller Company
of St. Paul, Minn. under the designation HL-1258 or H-2031. The
attachment means will preferably comprise an open pattern network
of filaments of adhesive as is disclosed in U.S. Pat. No.
4,573,986, issued to Minetola, et al. on Mar. 4, 1986, and which is
incorporated herein by reference. An exemplary attachment means of
an open pattern network of filaments comprises several lines of
adhesive filaments swirled into a spiral pattern such as
illustrated by the apparatus and method shown in U.S. Pat. No.
3,911,173 issued to Sprague, Jr. on Oct. 7, 1975; U.S. Pat. No.
4,785,996 issued to Zwieker, et al. on Nov. 22, 1978; and U.S. Pat.
No. 4,842,666 issued to Werenicz on Jun. 27, 1989. Each of these
patents are incorporated herein by reference. Alternatively, the
attachment means may comprise heat bonds, pressure bonds,
ultrasonic bonds, dynamic mechanical bonds, or any other suitable
attachment means or combinations of these attachment means as are
known in the art.
One disposable absorbent article in which the soft, strong nonwoven
of the present invention may be used are diapers. As used herein,
the term "diaper" refers to an absorbent article generally worn by
infants and incontinent persons that is worn about the lower torso
of the wearer. It should be understood, however, that the present
invention is also applicable to other absorbent articles such as
feminine hygiene or catamenial pads such as sanitary napkins and
pantiliners, and incontinence pads including diapers, and the
like.
FIG. 4 is a plan view of the diaper 400 of the present invention in
its flat-out, uncontracted state (i.e., with elastic induced
contraction pulled out) with portions of the structure being
cut-away to more clearly show the construction of the diaper 400
and with the portion of the diaper 400 which faces away from the
wearer, the outer surface, oriented towards the viewer. As shown in
FIG. 4, the diaper 400 preferably comprises a liquid pervious
topsheet 50; a liquid impervious backsheet 60 joined with the
topsheet; an absorbent core 70 positioned between the topsheet 50
and the backsheet 60, the absorbent core 70 having a garment
surface 72, a body surface 74, side edges 76, waist edges 78, and
ears 71. The diaper 400 preferably further comprises elasticized
leg cuffs 80; an elastic waist feature multiply designated as 90;
and a fastening system generally multiply designated as 110.
The diaper is shown in FIG. 4 to have an outer surface 42, an inner
surface 44 opposed to the outer surface 42, a first waist region
46, a second waist region 48, and a periphery 41 which is defined
by the outer edges of the diaper 400 in which the longitudinal
edges are designated 43 and the end edges are designated 45. (While
the skilled artisan will recognize that a diaper is usually
described in terms of having a pair of waist regions and a crotch
region between the waist regions, in this application, for
simplicity of terminology, the diaper 400 is described as having
only waist regions including a portion of the diaper which would
typically be designated as part of the crotch region). The inner
surface 44 of the diaper comprises that portion of the diaper 400
which is positioned adjacent to the wearer's body during use (i.e.,
the inner surface 44 generally is formed by at least a portion of
the topsheet 50 and other components that may be joined to the
topsheet 50). The outer surface 42 comprises that portion of the
diaper 400 which is positioned away from the wearer's body (i.e.,
the outer surface generally is formed by at least a portion of the
backsheet 60 and other components that may be joined to the
backsheet 60). (As used herein, the portion of the diaper 400 or
component thereof which faces the wearer is also referred to as the
body surface. Similarly, the portion facing away from the wearer is
also referred to herein as the garment surface.) The first waist
region 46 and the second waist region 48 extend, respectively, from
the end edges 45 of the periphery 41 to the lateral centerline 47
of the diaper. FIG. 4 also shows the longitudinal centerline
49.
FIG. 4 shows a preferred embodiment of the diaper 400 in which the
topsheet 50 and the backsheet 60 have length and width dimensions
generally larger than those of the absorbent core 70. The
elasticized leg cuffs 80 and the backsheet 60 extend beyond the
edges of the absorbent core to thereby form the periphery 41 of the
diaper 400.
Diapers of the present invention can have a number of well known
configurations. Exemplary configurations are described generally in
U.S. Pat. No. B1 3,860,003 issued to Buell on Apr. 18, 1989; U.S.
Pat. No. 5,151,092 issued to Buell et al. on Sep. 29, 1992; and
U.S. Pat. No. 5,221,274 issued to Buell et al. on Jun. 22, 1993.
Each of these patents is incorporated herein by reference. Other
diaper configurations to which the present invention can be readily
adapted are described in co-pending U.S. patent application Ser.
No. 08/203,456; filed on Feb. 28, 1994, and incorporated herein by
reference. The topsheet 50 and backsheet 60 can be readily adapted
by the skilled artisan to include the soft, strong nonwoven of the
present invention.
A preferred topsheet 50 for the diaper 400 is the soft, strong
nonwoven described herein. Such a topsheet is particularly soft
such that it tends to provide improved wearer comfort, including
reduced potential for irritation. Where the nonwoven is permanently
stretched to form apertures as described herein, the topsheet is
particularly effective in absorbing viscous body fluids, such as
feces. The topsheet 50 of diaper 400 may be made of a hydrophobic
material to isolate the wearer's skin from liquids which have
passed through the topsheet and are contained in the absorbent core
(i.e., to prevent rewet). If the topsheet is made of a hydrophobic
material, at least the upper surface of the topsheet is preferably
treated to be hydrophilic so that liquids will transfer through the
topsheet more rapidly. Such treatment and hydrophilicity is
described above in reference to treatment of the soft, strong
nonwoven of the present invention, which description is also
applicable to topsheet materials other than the nonwoven of the
present invention.
In a preferred embodiment, the backsheet 60 of the diaper 400
includes the soft, strong nonwoven of the present invention. More
preferably, the soft, strong nonwoven is combined with a polymeric
material to improve the fluid barrier properties of the backsheet
as previously described. The backsheet 60 preferably. has a
modified hourglass shape extending beyond the absorbent core 70 a
minimum distance of about 1.3 cm to about 6.4 cm (about 0.5 to
about 2.5 inch) around the entire diaper periphery.
The absorbent core 70 may take on any size or shape that is
compatible with the diaper 400. One preferred embodiment of the
diaper 400 has an asymmetric, modified T-shaped absorbent core 70
having ears 71 in the first waist region 46 but a generally
rectangular shape in the second waist region 48. Exemplary
absorbent structures for use as the absorbent core that have
achieved wide acceptance and commercial success are described in
U.S. Pat. No. 4,610,678 entitled "High-Density Absorbent
Structures" issued to Weisman et al. on Sep. 9, 1986; U.S. Pat. No.
4,673,402 entitled "Absorbent Articles With Dual-Layered Cores"
issued to Weisman et al. on Jun. 16, 1987; U.S. Pat. No. 4,888,231
entitled "Absorbent Core Having A Dusting Layer" issued to Angstadt
on Dec. 19, 1989; and U.S. Pat. No. 4,834,735, entitled "High
Density Absorbent Members Having Lower Density and Lower Basis
Weight Acquisition Zones", issued to Alemany et al. on May 30,
1989. The absorbent core may further comprise the dual core system
containing an acquisition/distribution core of chemically stiflened
fibers positioned over an absorbent storage core as detailed in
U.S. Pat. No. 5,234,423, entitled "Absorbent Article With Elastic
Waist Feature and Enhanced Absorbency" issued to Alemany et al., on
Aug. 10, 1993; and in U.S. Pat. No. 5,147,345, entitled "High
Efficiency Absorbent Articles For Incontinence Management" issued
to Young et al. on Sep. 15, 1992. All of these patents are
incorporated herein by reference.
In a preferred embodiment, the diaper 400 further comprises
elasticized leg cuffs 80 for providing improved containment of
liquids and other body exudates; an elastic waist feature 90 that
provides improved fit and containment; and a fastening system 110
which forms a side closure which maintains the first waist region
46 and the second waist region 48 in an overlapping configuration
such that lateral tensions are maintained around the circumference
of the diaper to maintain the diaper on the wearer. The diaper 400
may also comprise elasticized side panels (not shown) in the waist
regions 46 and 48 to provide an elastically extensible feature that
provides a more comfortable and contouring fit and more effective
application of the diaper 400.
The elasticized leg cuffs 80 provide improved containment of
liquids and other body exudates. Each elasticized leg cuff 80 may
comprise several different embodiments for reducing the leakage of
body exudates in the leg regions. (The leg cuff can be and is
sometimes also referred to as leg bands, side flaps, barrier cuffs,
or elastic cuffs.) For example, U.S. Pat. No. B1 3,860,003 issued
to Buell on Jan. 14, 1975, describes a disposable diaper which
provides a contractible leg opening having a side flap and one or
more elastic members to provide an elasticized leg cuff (gasketing
cuff). U.S. Pat. No. 4,909,803, issued to Aziz, et al. on Mar. 20,
1990 describes a disposable diaper having "stand-up" elasticized
flaps (barrier cuffs) to improve the containment of the leg
regions. U.S. Pat. No. 4,695,278, issued to Lawson on Sep. 22,
1987, describes a disposable diaper having dual cuffs including a
gasketing cuff and a barrier cuff. U.S. Pat. No. 4,704,115, issued
to Buell on Nov. 3, 1987, discloses a disposable diaper or
incontinent garment having side-edge-leakage-guard gutters
configured to contain free liquids within the garment. An
additional leg cuff configuration is disclosed in U.S. Pat. No.
4,795,454, issued to Dragoo on Jan. 3, 1989. Each of these patents
is incorporated herein by reference.
While each elasticized leg cuff 80 may be configured so as to be
similar to any of the leg bands, side flaps, barrier cuffs, or
elastic cuffs described above, it is preferred that each
elasticized leg cuff comprise at least an inner barrier cuff
comprising a barrier flap and a spacing elastic member such as
described in the above-referenced U.S. Pat. No. 4,909,803. In a
preferred embodiment, the elasticized leg cuff 80 additionally
comprises an elastic gasketing cuff with one. or more elastic
strands positioned outboard of the barrier cuff such as described
in the above-referenced U.S. Pat. No. 4,695,278.
In a preferred embodiment, the leg cuff material comprises the
soft, strong nonwoven of the present invention. The nonwoven can be
used as the leg cuff material with or without combination with a
polymeric material to improve the fluid barrier properties of the
leg cuff material. However, the nonwoven should have a hydrostatic
head pressure of at least about 100 mm when measured according to
Method 5514 Federal Test Methods Standard #191A, incorporated
herein by reference.
The elasticized waist feature 90 preferably comprises an
elasticized waistband (not shown) that may be constructed in a
number of different configurations including those described in
U.S. Pat. No. 4,515,595 issued to Kievit et al. on May 7, 1985;
U.S. Pat. No. 5,026,364 issued to Robertson on Jun. 25, 1991; and
the above referenced U.S. Pat. No. 5,151,092 issued to Buell et al.
on Sep. 29, 1992, each of these references being incorporated
herein by reference.
The elasticized side panels may be constructed in a number of
configurations. Examples of diapers with elasticized side panels
positioned in the ears (ear flaps) of the diaper are disclosed in
U.S. Pat. No. 4,857,067, issued to Wood, et al. on Aug. 15, 1989;
U.S. Pat. No. 4,381,781, issued to Sciaraffa, et al. on May 3,
1983; U.S. Pat. No. 4,938,753, issued to Van Gompel, et al. on Jul.
3, 1990; and U.S. Pat. No. 5,151,092, issued to Buell et al. on
Sep. 29, 1992; each of which are incorporated herein by
reference.
Exemplary fastening systems 110 are disclosed in U.S. Pat. No.
4,846,815, issued to Scripps on Jul. 11, 1989; U.S. Pat. No.
4,894,060, issued to Nestegard on Jan. 16, 1990; U.S. Pat. No.
4,946,527, issued to Battrell on Aug. 7, 1990; U.S. Pat. No.
3,848,594, issued to Buell on Nov. 19, 1974; U.S. Pat. No.
4,662,875, issued to Hirotsu et al. on May 5, 1987; and U.S. Pat.
No. 5,151,092, issued to Buell et al. on Sep. 29, 1992; each of
which is incorporated herein by reference.
The diaper 400 is preferably applied to a wearer by positioning one
of the waist regions of the diaper, preferably the second waist
region 48, under the wearer's back and drawing the remainder of the
diaper between the wearer's legs so that the other waist region,
preferably the first waist region 46, is positioned across the
front of the wearer. The fastening system is then applied to effect
a side closure.
The soft, strong nonwoven of the present invention can be employed
in several other disposable absorbent articles, in the manner
previously described generally or in relation to diapers. For
example, the soft, strong nonwoven can be employed as the topsheet
or backsheet or as a component of either or both of these members
in several other disposable absorbent articles. Exemplary
additional disposable articles to which the present invention can
be adapted include sanitary napkins, pantiliners, training pants,
and incontinent articles.
Preferred sanitary napkin configurations applicable to the present
invention are described generally in the above referenced and
incorporated U.S. Pat. Nos. 4,950,264 and 5,009,653; and in U.S.
Pat. No. 4,321,924, "Bordered Disposable Absorbent Article," issued
to Ahr on Mar. 30, 1982; U.S. Pat. No. 4,425,130, "Compound
Sanitary Napkin," issued to DesMarais on Jan. 10, 1984; U.S. Pat.
No. 4,589,876, "Shaped Sanitary Napkin With Flaps," issued to Van
Tilburg on Aug. 18, 1987; U.S. Pat. No. 4,608,047, "Sanitary Napkin
Attachment Means," issued to Mattingly on Aug. 26, 1986; U.S. Pat.
No. 4,687,478, "Shaped Sanitary Napkin With Flaps," issued to Van
Tilburg on Aug. 18, 1987; U.S. Pat. No. 4,834,735, "High Density
Absorbent Members Having Lower Density and Lower Basis Weight
Acquisition Zones," issued to Alemany et al. on May 30, 1989; U.S.
Pat. No. 4,917,697, issued to Osborn et al. on Apr. 17, 1990; U.S.
Pat. No. 5,308,346, "Elasticized Sanitary Napkin," issued to
Sneller, et al. on May 3, 1994; European Patent Application No. 0
198 683, The Procter & Gamble Company, published Oct. 22, 1986
in the name of Duenk, et al.; PCT Patent Publication WO 93/11725,
"Absorbent Article Having Fused Layers," published in the name of
Cree, et al. on Jun. 24, 1993; and in copending and co-assigned
U.S. patent application Ser. No. 08/289,084, filed May 6, 1994 in
the name of Cree et al. Each of these patents, publications and
applications are hereby incorporated herein by reference.
Exemplary pantiliners for which the present invention may be
adapted are disclosed in U.S. Pat. No. 4,738,676 entitled
"Pantiliner" issued to Osborn on Apr. 19, 1988, which patent is
incorporated herein by reference.
The term "training pant", as used herein, refers to disposable
garments having fixed sides and leg openings. Training pants are
placed in position on the wearer by inserting the wearer's legs
into the leg openings and sliding the training pant into position
about the wearer's lower torso. Suitable training pants to which
the present invention can be adapted are disclosed in U.S. Pat. No.
5,246,433, issued to Hasse, et al. on Sep. 21, 1993.
The term "incontinence article" refers to pads, undergarments (pads
held in place by a suspension system of same type, such as a belt,
or the like), inserts for absorbent articles, capacity boosters for
absorbent articles, briefs, bed pads, and the like regardless of
whether they are worn by adults or other incontinent persons.
Suitable incontinence articles to which the present invention can
be adapted are disclosed in U.S. Pat. No. 4,253,461 issued to
Strickland, et al. on Mar. 3, 1981; U.S. Pat. Nos. 4,597,760 and
4,597,761 both issued to Buell on Jul. 1, 1986; the
above-referenced and incorporated U.S. Pat. No. 4,704,115; U.S.
Pat. No. 4,909,802 issued to Ahr, et al. on Mar. 20, 1993; U.S.
Pat. No. 4,964,860 issued to Gipson, et al. on Oct. 23, 1990; and
in U.S. Pat. No. 5,304,161 entitled "Absorbent Article Having Rapid
Acquiring Multiple Layer Absorbent Core" issued to Ahr on Apr. 19,
1994. Each of these patents are incorporated herein by
reference.
EXAMPLES
Consolidate a polyethylene melt-spunbonded nonwoven, designated as
#86964-S from Polybond Co. of Waynesboro, Va., having a filament
denier in the range of 1.5 to 10 and basis weight of 1
ounce/yard.sup.2, by calender thermalbond rolls with 225
pins/inch.sup.2 to provide a nonwoven having a CD width of about 8
inches and a bond area of about 14%.
Stretch the consolidated nonwoven in one stage via a stretching
apparatus such as shown in FIGS. 1-3 to a CD width of about 12
inches, to reduce the basis weight by 31%, to reduce the low strain
modulus by 70%, to substantially improve softness of hand as shown
by a loss in MD and CD tensile and, especially, loss in the low
strain MD modulus, without forming apertures.
Alternatively, stretch the nonwoven in one stage via a stretching
apparatus such as shown in FIGS. 1-3 to a CD width of 14.5-16.5
inches, to reduce the basis weight by 41% and to form apertures at
a frequency of about 20/in.sup.2 and a size of about 0.02" by about
0.04" (0.008 in.sup.2), to substantially improve softness of hand
as shown by a loss in MD and CD tensile and loss in low strain MD
modulus, and to maintain tensile values sufficiently high such that
the resultant nonwoven maintains its integrity when used as a
topsheet in a diaper of catamenial pad. The aforementioned
nonwovens will have properties as shown in Table I.
TABLE I
__________________________________________________________________________
MD basis tensile CD elongation modulus at porosity, % weight
strength, at maximum CD elongation 1% ft.sup.3 air/ft.sup.2 -
apertures stretched (g/yd.sup.2) g/in tensile, % to break, %
elongation minute* formed
__________________________________________________________________________
0 28 1544 (MD) 53 280 10.8 480 no 825 (CD) 31 19.3 635 (MD) 152
>160 3.2 742 no 612 (CD) 41 16.5 354 (MD) 68 >70 2.1 1115 yes
509 (CD)
__________________________________________________________________________
*as measured on a U.S. Testing Co. Inc., Model 9025 Air
Permeability Tester
While particular embodiments of the present invention have been
illustrated and described, it would be obvious to those skilled in
the art that various other changes and modifications can be made
without departing from the spirit and scope of the invention. It is
therefore intended to cover in the appended claims all such changes
and modifications that are within the scope of this invention.
* * * * *